<HTML><HEAD><TITLE>decval(++ElemSpec)</TITLE>
</HEAD><BODY>[ <A HREF="index.html">Non-logical Variables, Arrays, Bags, Shelves and Stores</A> | <A HREF="../../index.html">Reference Manual</A> | <A HREF="../../fullindex.html">Alphabetic Index</A> ]
<H1>decval(++ElemSpec)</H1>
Decrements the contents of the visible non-logical variable or array element ElemSpec by one.
<DL>
<DT><EM>ElemSpec</EM></DT>
<DD>Atom or ground compound term whose arguments are non negative integers.
</DD>
</DL>
<H2>Description</H2>
   Decrements by one the value of ElemSpec that must be of type integer.
<P>
   If ElemSpec is an atom, it must specify a non-logical variable visible
   from the caller module.
<P>
   If ElemSpec is a compound term, it must specify an element visible
   array.  All its arguments must be non negative integer smallers than the
   bound specified with array/1/2 or variable/1.
<P>

<H3>Modes and Determinism</H3><UL>
<LI>decval(++) is det
</UL>
<H3>Modules</H3>
This predicate is sensitive to its module context (tool predicate, see @/2).
<H3>Exceptions</H3>
<DL>
<DT><EM>(4) instantiation fault </EM>
<DD>ElemSpec is not instantiated.
<DT><EM>(5) type error </EM>
<DD>ElemSpec is a structure whose arguments are not all integers.
<DT><EM>(5) type error </EM>
<DD>ElemSpec is neither an atom nor a ground structure.
<DT><EM>(5) type error </EM>
<DD>The value or type of ElemSpec is not integer.
<DT><EM>(6) out of range </EM>
<DD>Array index in ElemSpec is out of bounds.
<DT><EM>(41) array or global variable does not exist </EM>
<DD>ElemSpec does not designate an existing array, variable or reference.
</DL>
<H2>Examples</H2>
<PRE>
Success:
      [eclipse]: local(array(a(4), prolog)),
              setval(a(0), -2),
              decval(a(0)),
              getval(a(0),X).
      X = -3
      yes.

      [eclipse]: local(array(g(4, 5), integer)),
              decval(g(3, 2)),
              getval(g(3, 2), X).
      X = -1
      yes.

      [eclipse]: setval(a, 3),
              decval(a),
              getval(a, X).
      X = 2
      yes.

Error:
      decval(X).                          (Error 4).
      setval(a, 2.0),
          decval(a).                      (Error 5).
      local(array(a(2), float)),
          decval(a(1)).                   (Error 5).
      local(array(a(2))),
          decval(a(2)).                   (Error 6).
      decval(no_var).                     (Error 41).
      decval(noarray(2, 4)).              (Error 41).



</PRE>
<H2>See Also</H2>
<A HREF="../../kernel/storage/getval-2.html">getval / 2</A>, <A HREF="../../kernel/storage/incval-1.html">incval / 1</A>, <A HREF="../../kernel/storage/array-1.html">array / 1</A>, <A HREF="../../kernel/storage/array-2.html">array / 2</A>, <A HREF="../../kernel/storage/variable-1.html">variable / 1</A>, <A HREF="../../kernel/storage/setval-2.html">setval / 2</A>
</BODY></HTML>
